Lubricating composition



Patented July 15, 1952 LUBRICATING COMPOSITION Seaver Ames Ballard, Orinda, Rupert Clarke Morris, Berkeley, and John L. Van Winkle, San Lorenzo, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application November 1, 1948,, Serial No. 57,836

12 Claims. "(01. 25248.6)

This invention relates to improved lubricating materials, and more particularly, relates to improved organic compounds having superior lubricating characteristics, said compounds containing thioether groups.

Mineral oil lubricants, such as those made from paraffinbase or naphthenic base petroleums, are useful for most lubricating purposes when the conditions to which said lubricants are subjected are relatively mild. However, lubricantsof petroleum originare limited, in their utility by certain inherent properties or charao teristics. For example, especially when employed for aviation purposes, a lubricant is often subjected to wide temperature variations, such as hot ground temperatures and the extremely cold temperatures encountered in the atmosphere, say about 20,000 feet altitude. .In these circumstances, the ordinary mineral oil lubricants fail to function properly, either being too fluid when. warm, or hardening to a solid or semisolid state when cold.

The tendency of mineral oils to oxidize rapidly, especially in the presence of certain metallic substances such as copper, iron oxide, etc., is well known. While the addition of anti-oxidants corrects this adverse feature to a limited extent, in many instances mineral oil lubricants are unsatisfactory, due to sludge and gum formation, both of which phenomena are results of oxidation reactions.

Certain non-hydrocarbon substances of synthetic origin have been used for specialized lubrication purposes. For example, polymeric alkylene oxides, such as polymerized propylene oxide, have been used for lubricating purposes. Other similar polymers have found restricted use as substitutes for mineral oil lubricants. Some of these have hydroxyl or alkoxyl end groups on one or both ends of the polymeric chain. These various liquid polymeric lubricants have one or more properties which make their substitution for mineral oil advantageous. For example, the viscosity indices of many of them are relatively high, in comparison with those of mineral oils, and for this reason operate over a comparatively wide temperature range. However, due to the free hydroxyls or loosely bound terminal alkoxyl groups, the syntheic lubricants are usually unsatisfactory for many purposes, since they are unstable towards oxidizing influences, change their characteristics relatively rapidly during engine use, absorb water from the surrounding atmosphere, etc.

It is an object of this invention to provide improved non-mineral oil lubricants. It is another object of this invention to provide a non-petroleum lubricant having improved resistance to oxidation. It is a third object of this inventionto provide a process for preparing non-hydrocarbon lubricants having substantially no ability to absorb water. It is still another object of this invention to provide new lubricants which are thermally stable. Other objects will appear hereinafter.

In accordance with this invention, it has been found that liquid esters, and especially diesters, of bis(hydroxyalkyl) sulfides form unexpectedly superior lubricating compositions having high viscosity indices, low pour points, good thermal stability and high resistance to oxidizing infiuences. Still, in accordance with this invention, it has been found that esters of the above type, wherein each ester group contains at least six carbon atoms, are miscible with viscosity index improving agents such as high molecular weight polymeric esters of the acrylic acid series.

Again in accordance with this invention, it has.

been found that esters of the above-defined sulfides may be readily solubilized with methacrylate polymers by the inclusion of a diester of a dicarboxylic aliphatic ester regardless of the carbon content in the ester grouping of the sulfide.

The sulfides or thioethers which may be esterified and used as lubricants, in accordance with this invention, have a general formula may be straight chain or branched chain in configuration.

For example, the primary dihydroxy thioethers have the general formula wherein'the Rs are saturated aliphatic radicals.

Thioethersof this configuration are conveniently prepared by the abnormal condensation of unsaturated alcohols with hydrogen sulfide.

' Thus, when allyl alcohol and hydrogen sulfide are condensed in the presence of ultra-violet light at moderate temperatures, one of the products is bis(gamma-hydroxypropyl) sulfide.

A. typical preparation of this character is that tut on. prod c s Joy the above method include bis beta-hydroxyformula of the condensation of hydrogen sulfide with allyl alcohol, as follows:

Allyl alcohol (500 cc.) and hydrogen sulfide (124 g.) were mixed in a quartz tube and irradiated near a 250-watt mercury arc lamp for two hours. During the first hour the pressure rose from 140 lbs. per sq. in. to 190 lbs. per sq. in., after which it fell 160 lbs. per sq. in. In this time the temperature increased from 15 C. to 100 C., due in part to the exothermic character of the reaction, but mainly due to the heat from the mercury arc lamp. The product was subjected to fractional distillation, that part remaining in the still above 134 C. at 0.3 cm. Hg pressure being bis(garnma-hydroxypropyl) sulfide.

Suitable alcohols for the preparation of primary dihydroxy thioethers include isopropenyl alcohol, allyl alcohol, crotyl alcohol, methallyl alcohol, and their homolog analogs and substi- Dihydroxy thioethers formed ethyl), sulfide and bis(gamma-hydroxypropyl) ulfid Ifthe thioether has hydroxyl groups on other thanterminal carbons, the dihydroxy'thioethers include bis(alpha-hydroxyethyl) sulfide, -bis(alphaand beta-hydroxypropyl) sulfide.

Mixed'hydroxy thioethers are useful informing the esterified lubricants of the present invention. These include beta-hydr'oxyethyl-gam- .maehydroxypropyl sulfide, hydroxymethyl-betahydroxyethyl sulfide,v alpha-hydroxyethyl-alpha- :hydroxypropyl sulfide, as well as their homologs, analogs and derivatives. Higher 'thioethers of this class maybe prepared'having hydroxybutyl,

hydroxyamyl, .hydroxyhexyl, etc.,groups, including'the long-chain groups, such as the hydroxylauryl, hydroxystearyl, etc., groups.

"These hydroxythioethers having the general in which the Rs are similar saturated aliphatic radicals having from one to six carbon items are preferred in preparing the este'rified lubricants of the present invention.

This same type abnormal condensation of unsaturated alcohols With hydrogen sulfide is catalyzed by the presence of bases or organic peroxides such as tertiary'alkyl hydroperoxides, spechically, tertiary butyl hydroperoxide. Alkyl peroxy alkanes, such as, 2,2-bis(tertiary-butyl peroxy) butane also may be used. When basic catalysts (suchas alkali metal hydroxides or amines) or peroxide catalysts are used, branched configurations .result, since the addition takes place in the normal manner according to the Markownikoff rule. For example, when allyl alcohpl and aliphatic monocarboxylic acids having from two totwenty carbon atoms. and, preier'ablyfroin two to eight carbon atoms. The saturatedfattyacids are especially suitable, and those having from three. to eight carbon atomsform highly satisfactory lubricants. Typical acids are isopropicnic, Z-ethyl hexoic, oleic, stearic and their analogs homologs.

The esterified lubricants which comprise the present invention are formed by heating the acid, or acid derivative such as anhydride, chloride, etc, with the lubricant, usually in the presence of a catalyst or dehydrating agent. Catalysts useful when carrying out the esterification include zinc chloride, hydrogen chloride, concentrated sulfuric acid, p-toluene sulfonic acid, concentrated phosphoric acid, metallic oxides such as titanium oxide, etc.

The esterification may be carried out With or without a diluent being present. The diluent may be used merely to thin the mixture, especially if the lubricant is viscous. Again, it may be present as a solvent either for the catalyst, esteriiying agent or thioether. The diluent is usually a liquid boiling at about the temperature at which the esterification is to be conducted. In such a case, the diluent serves not only as a partial or completejsolvent for one or more of the reaction components, but acts as a temperature-controlling agent aswell'. The 'diluent preferably is an inert solvent such as hydrocarbon, including the hexanes, o'ctanes, d0- decanes, etc, and their isomers. ldixtures of diluents may be used' The esterification usually is: conducted at temperatures from about50" C. to about 200 C. when an anhydride is used as the esterifying agent. When the acid-chloride is employed, the

, esterification temperature will vary from about 10 C. to about 150 C. When'the esterification agent contains a long hydrocarbon chain, it may be relatively inactive and consequently requires prolonged reaction at elevated'temperatur'e with the lubricants in .order to effect substantially complete esterifioation.

The time necessary to complete the esterification will depend upon the esterificati'on agent, the identity of the lubricant, the identity of the catalyst and its ratio to the components; aswell as the temperature at which the esterification is conducted. Usually, it will require from 0.1 to 24 hours, preferably from 0.5 to 6hours, since this latter preferred range of esterification time allows adequate chance to maintain-control over the reaction. If the esterification is allowed to proceed too rapidly, the action may become violent, and a certain amount of decomposition may occur, with the resultant loss of product and formation of color bodies.

Subsequent to esterification, the esterifiewlubricant is purified by the removal. ofcatalysts, ex cess esterifying agents, solvents, water and color bodies. Catalysts and esteriiying agents may be removed, for example; by extracticn'with selected solvents, such as. water; dilute aqueous alkali, also by-use of ion-exchange resins, 'fullers' earth, etc. Solvents be fiashedjoiior' removed'byextrac tion: Water may be removed with dehydrating agents... or with heating under diminished pressure. The removal of colorbodies may beefiected with activated-carbon, percolation through activatedclays such as iullers earth, mild oxidation, hydrogenation, etc. preferred combination of decolorizing steps is percolation through an activated clay'followed by hydrogenation. y In summary, the esters forming'the lubricants of the present invention have the typical formula wherein each R is an aliphatic hydrocarbon radical havingfrom two to twenty carbon atoms.

acterizes many of them. Moreover, the viscosity 5 indices, especially of the unbranched esters, have been found to be especially high. The dipropionate of bis(gamma-hydroxypropyl) sulfide has a viscosity index of 101 and a pour point lower than 65 F. Esters of the subject thioethers having at least six carbon atoms in the ester group are compatible with viscosity index improving agents such as high molecular weight esters of the acrylic acid series. The latter compounds are commercially available under the trade name Acryloid. They are understood to be a mixture of polymerized esters of methacrylic acid having a molecular weight range between 10,000 and 25,000. The ester groups of the methacrylate polymers are derived from aliphatic alcohols having from two to ten carbon atoms. Those having from two to four carbon atoms, namely, ethyl, propyl and butyl alcohols, form the most effective polymeric methacrylate viscosity index improvers. The viscosity properties of 'bis(2-ethylhexoyl-gamma-oXy-propyl) sulfide, both with and without 2% Acryloid, are

as follows: I

Without With Acryloid Acryloid Viscosity, Centipoises at 100 F 10.63 13.50 Viscosity, Centipoises at 210 F 2. 62 3. 31 Viscosity Index 83 132 Four Point, F., lower than... 65

A representative lubricating composition according to the invention comprises 90-99% by weight of a liquid aliphatic ester of a bis(hydroxyalkyl) sulfide and 1-10% by weight of a polymerized methacrylic acid ester having a molecular'weight between 10,000 and 25,000.

In order to solubilize methacrylate polymers in thioethers having ester end groups as low as two carbon atoms, diesters of aliphatic carboxylic acids having four to twelve carbon atoms may be added. Examples of solubilizing esters of this variety include the 2-ethylhexyl diesters of sebacic acid and of adipic acid. The corresponding decyl and dodecyl esters of the same or similar acids are also effective. The dibasic acids from which the esters are to be formed should have from four to twelve carbon atoms, preferably in a straight chain. An example of this type of composition comprises the following:

This composition had the following viscosity characteristics Viscosity, centipoises 100" F 9.25 Viscosity, centipoises 210 F 2.84 Viscosity index 169 Representative lubricating compositions in accordance with this embodiment of the invention comprise: I

50-90% by weight of a liquid aliphatic ester of bis (hydroxyalkyl) sulfide, I

-40% by weight of a liquid aliphatic diester of a dicarboxylic acid, and

1-10 by weight of a polymerized methacrylic acid ester having a molecular weight of 10,000 to 25,000.

Esters of the above description are especially jet lubricants. They have been found to be especially effective, also, in spur-gear mechanisms. For example, the diesters of bis(gamma-hydroxy propyl) sulfide did not start to score in a spurgear mechanism until a load of 50 lbs. had been applied. A mineral oil of similar viscosity started to score under a load of 5 lbs; The following example describes the preparation of a typical ester:

Equal parts by weight of bis(hydroxypropyl) sulfide and toluene were heated with 15-20% of an excess of propionic acid for the formation of the dipropionate ester. Para-toluene sulfonic acid in 1% concentrate based on the sulfide was present as a catalyst. The mixture was heated until water ceased distilling, a period of about four hours. The reaction mixture was Washed with potassium carbonate and Water and then was subjected to distillation to remove toluene and any remaining moisture. The product was found to have the following properties:

Viscosity, cps. at 40 F 320 Viscosity, cps. at 100 F 4.74 Viscosity, cps. at 210 F 1.61 Viscosity index 101 Four point, F lower than 50-90% by weight of a liquid aliphatic ester of bis(hydroxyalkyl) sulfide, the hydrocarbon units 7 of said ester being aliphatic hydrocarbon radicals having from 2 to 20 carbon atoms each, 10-40% by weight of a liquidaliphaticdiester of a dicarboxylic acid and 1-10% by weight of a polymerized methacrylic acid ester having a molecular weight of 10,000 to 25,000.

3. A stable lubricating composition comprising about 52.8% by weight of bis(acetyl-oxy-propyl) sulfide, about 44.4% by weight of bis(2-ethy1- hexyl) sebacate and about 2.8% by weight of a polymerized alkyl methacrylate havinga molecular Weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to, 10 carbon atoms.

4. A stable synthetic lubricating composition consisting essentially of a major portion oi a liquid aliphatic ester formed between a bis(hydroxyalkyl) sulfide, the hydroxy alkyl radicals of said sulfide each having from 2 to 20 carbon atoms andan aliphatic carboxylic acid having from 2 to 20 carbon atoms; and 1-10% by weight of a polymerized alkyl acrylate having a molecular weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms. a

5. A stable synthetic lubricating composition consisting essentially of a major proportion of a .7 liquidlaliphaticester formed between a bis(hydrox'yalkyl) sulfide, the hydroxy alkyl radicals of said sulfide each having from 2 to 20 carbon atoms and oleic'acid; and 140% by weight of a polymerized alkyl acrylate having a molecular weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to carbon atoms.

6. 'A stable synthetic lubricating composition consisting essentially of a major proportio of a liquid aliphatic ester of a bis(hydroxyalkyl) sulfide, the hydroxy alkyl radicals of said sulfide each having from 2 to 20 carbon atoms and an aliphatic saturated carboxylic acid having from 2 to 8 carbon atoms; and 1-10% by weightlof a polymerized alkyl acrylate having a molecular weight of "10,000 to 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms.

'7. A stable lubricating composition consisting essentially of a major proportion of a liquid aliphatic ester of a bis(hydroxyalkyl) sulfide, the hydrocarbon units of said sulfide being aliphatic hydrocarbon radicals having from 2-20 carbon atoms, said sulfide being esterified with a saturated fatty acid, 10-40% by weight of a liquid aliphatic ester formed between a dicarboxylic acid having from 4 to 12 carbon atoms and an aliphatic alcohol having from 8 to 12 carbon atoms; and 1-10% by weight of a polymerized ester of the acrylic acid series, said polymerized ester having a molecular weight between 10,000 and 25,000. .2 f. "8. 'Astable synthetic lubricating composition consisting essentially of a major amount of a liquid aliphatic ester formed between a bis(hy droxyalkyl) sulfide, the 'hydroxy all iyl radicals of said sulfide each having from 2 to 20 carbon atoms and an aliphatic saturated carboxylic acid having from 2 to 20 carbon atoms; and 110% by weight of a polymerized alkyl acrylate having a molecular weight'of 10,000 to 25,000 and where- 'in the alkyl radical has ifroin 2 to 4 carbon atoms. 9.'A 'stablesynthetic lubricating composition egattas 7 consisting essentially of a major proportion of a liquid 2,-ethylhexoate of a bis(hydroxyalkyl) sul fide, the hydroxy alkyl radicals of said sulfide each having from 2 to 20 carbon atoms; and 1-10% by weight of a polymerized alkyl acrylate having a molecular weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms. a

10. A stable synthetic lubricating. composition consisting essentially of a major proportion of a liquid 2-ethylhexoate of bis(gamma-hydroxypropyl) sulfide; and by weight of a polymerized alkyl acrylate having a molecular weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms.

11. A stable synthetic-lubricating composition consisting essentiallyiof a major proportion of a liquid propionate of bis(gamma'-hydroxypropyl) sulfide; and 110% by weight of a polymerized alkyl acrylate having a molecular weight of 10,000 to 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms. 7

12. A stable synthetic lubricating composition consisting essentially of a major proportion ofa liquid acetate of bis(gamma-hydroxypropyl) sulfide; and 1-10% by weight of a polymerized alkyl acrylate having a molecular weight'of 10,000Ito 25,000 and wherein the alkyl radical has from 2 to 10 carbon atoms.

, SEAVER AMES BALLARD.

RUPERT CLARKE MORRIS. JOHN L. VAN WINKLE,

V REFEBENES or an 7 "The following references are of record in the file of this patent: g

UNITED STATES PATENTS v I Date a Number Name 2,356,586 Hentrich 1 Aug. 22, 1944 2,417,281 'Wasson et al. 'Mar. 11, 1947 2,451,895 White Oct.19, 1940 

1. A STABLE LIQUID LUBRICATING COMPOSITION COMPRISING 90-99% BY WEIGHT OF A LIQUID ALIPHATIC ESTER OF A BIS(HYDROXYALKYL) SULFIDE, THE HYDROCARBON UNITS OF SAID ESTER BEING ALIPHATIC HYDROCARBON RADICALS HAVING FROM 2 TO 20 CARBON ATOMS EACH, AND 1-10% BY WEIGHT OFF A POLYMERIZED METHACRYLIC ACID ESTER HAVING A MOLECULAR WEIGHT BETWEEN 10,000 AND 25,000. 